1. Field of the Invention
This invention is related to radio frequency (RF) antennas, and particularly to planar dual band array antennas operable in adverse weather conditions, and fully integrated with the RF housing, including baseband electronics.
2. Background of the Invention
The operation of a mini-hub and multiple remote terminals in a hitless or a non-redundant configuration, along with multiple mini-hub satellite earth stations communicating with numerous remote satellite earth stations are described in the parent applications. The present invention is concerned with flat array antennas that operate in a wide range of weather conditions and physically coupled to the RF housing and baseband at electronics in a fully integrated outdoor configuration.
In order to maintain communication throughout all types of weather conditions, antennas typically use a dish that is angled in such a manner that the dish will not collect rain or snow. In locations with heavy snow various methods are used to xe2x80x9cheatxe2x80x9d the antenna. Further, the dish is sized to ensure that even in poor transmission conditions, the signal strength will be large enough to receive a clear signal.
However, dish antennas tend to be heavy, bulky devices that take up a large amount of space and often require concrete foundations. Further, the dish antennas must sometimes be moved to align the dish with the satellite that the dish communicates with, which requires not only large motors, but a large spatial volume in order to operate. The RF section consisting of the feedhorn, up-down converters, and other interconnections are exposed to the weather. At higher frequencies used in satellite communications this contributes to poor reliability.
Previous attempts at fabricating flat array antennas have had problems with reliable RF transmissions because precipitation, whether it is rain, snow, or sleet, have greatly reduced the signal strength to unacceptable levels for satellite transmission and reception. These conditions would cause communications to cease during periods of precipitation, which would be unacceptable for users that a need reliable, consistent communications link.
It is desirable to have a small flat antenna that can send and receive signals in all types of weather conditions. The flat array antenna that can operate in all weather conditions is also desirable in terms of size, maneuverability, and cost.
An additional adverse environmental condition on a satellite earth station antenna is its exposure to direct sunlight. Such exposure tends to unduly heat the electronics incorporated into a satellite earth station. Such an increase in operating temperature for the electronics may cause reliability problems, as well as adversely effects its operating performance. Therefore, there is need for an RF antenna housing that protects or shields the earth station antenna electronics from significant exposure to direct sunlight.
An additional drawback of prior art RF antennas is that the baseband electronics is remotely located from the RF antenna housing. More specifically, in prior art antenna systems, baseband electronics is located indoors, whereas the RF antenna housing is located outdoors. Because the baseband electronics is located in a different area than the RF antenna housing, relatively long cables are required to couple the RF antenna housing to the baseband electronics. These cables can have a length of up to 1,000 feet. As a result, noise creeps in the antenna system via the long cable. In addition, the RF signals residing in the long cables can also interfere with sensitive indoor electronics through electromagnetic interference (EMI). Furthermore, the long cables further attenuates the RF signals resulting in a lower signal-to-noise ratio. It would be desirable that the signal residing in the long cables be in digital format and at a lower baseband frequency. Accordingly, there is a need for a system which eliminates this long cable connection for transmitting RF signals.
Yet another drawback of flat array antenna systems is that they require a flat array patch for transmitting that is separate from the flat array patch for receiving. Because two flat array patches are required, prior art flat array antenna systems typically require a relatively large footprint to accommodate both antenna patches. As a result, prior art antenna systems take up substantial amount of space, which is undesirable. Accordingly, there is a need for an antenna system that uses a single flat array antenna patch to serve both as a transmitter and a receiver for the system.
According to the invention, a planar antenna for all weather applications comprises. an antenna array, a radome with appropriate dielectric constant and mechanical strength, properly spaced from the array, and a housing. The antenna array comprises at least one radiating element that interfaces to waveguides or microstrip feed structures.
The radiating elements, which can be either dual-fed patch array (with the same patch serving to transmit for example ku-band and receive x-band) or microstrip dipole transmission lines or slotted waveguides, are microstrip fed or are aligned to the waveguide corporate feed structure to ensure proper coupling. The array can also be aligned to each other to assure that the main beams (lobes) of the array pattern are aligned on a common target, typically a satellite.
The parent application describes remote USAT terminal communications equipment which utilizes a local reference frequency for acquisition and tracks the received carrier frequency during normal communications. The local reference frequency is voltage controlled to maintain a close match to the carrier frequency.
One method of practicing the present invention is to screen print electrical RF circuits on flexible dielectric substrate materials to provide the ability to manufacture precision arrays of various sizes. This provides a cost-effective antenna even in small quantities. The present invention thus provides a low-cost flat antenna array. The configuration facilitates the use of flexible printed wiring materials in the construction of flat antenna arrays.
Another method. of practicing the present invention is to make a slotted waveguide array. The slots are precision machined or stamped and can vary in size depending on the desired frequency and gain for the antenna.
Accordingly, an object of the present invention is to provide a flat antenna array of radiating elements that is operable in a wide range of weather conditions.
Also disclosed is an antenna array comprising a top dielectric having a top metallization layer patterned into an antenna array patch and a first feed network having a first port, the first feed network configured to couple signals within a first frequency band between the antenna array patch and the first port. The antenna array also includes a bottom dielectric including a bottom metallization layer patterned into a second feed network having a second port and a radiating element, wherein the second feed network is configured to couple signals within a second frequency band between the second port and the radiating element. The antenna array further includes an intermediate metallization layer disposed between the top dielectric and the bottom dielectric, wherein the intermediate metallization layer includes openings for coupling signals within the second frequency band between the antenna array patch and the second feed network.
Further objectives and advantages of this invention will become apparent from the following description and drawings.